(1) Field of the Invention
The present invention relates to a lithium oxide based amorphous material and a process for the preparation thereof.
(2) Description of the Prior Art
The interest in a solid lithium ion conductor has recently been increasing. Especially, utilization of a lithium ion conductor as a solid electrolyte of a lithium cell or an electrolyte of an electrochromic display device has been developed. In the former case, since the requirement for reduction of the thickness of the cell has been increasing with recent requirements for minimization of the sizes of electronic devices and reduction of the thickness thereof, application fields have been abruptly expanded. For example, a lithium cell comprising an evaporated film of LiI as a solid electrolyte is proposed in J. Electro. Chem. Soc., Vol. 116, No. 10, pages 1452 (1969). This evaporated film, however, consists of a polycrystalline body having a thickness of about 10 to about 15 .mu.m, and the ionic conductivity of the film is about 10.sup.-7 mho.multidot.cm.sup.-1.
In the latter case, the above-mentioned solid electrolyte is used so as to render the electrochromic display device totally solid and stabilize the structure of the device.
In both the cases, it has been desired to develop a solid electrolyte having a high ionic conductivity and being stable in an ordinary atmosphere. At the present, however, since the resistance to the ionic conduction in the solid electrolyte is high, no satisfactory device of the above-mentioned type has practically been developed.
As means for increasing the ionic conductivity of the above-mentioned device, there can be considered a method in which the solid electrolyte is formed into a thin film to geometrically reduce the resistance. According to the conventional ceramic technique, however, it is difficult to form a thin film having a thickness smaller than 10 .mu.m. Furthermore, according to the conventional film-forming technique such as the CVD method or sputtering method, a thin film having a high ionic conductivity cannot be obtained. The reason is that the temperature for the synthesis of an oxide based solid electrolyte is high, an alkali metal oxide is lost by evaporation or the like during formation of a thin film and control of the composition is therefore difficult.
On the other hand, the following reference is cited to show the state of the art: that is, J. Electro. Chem. Soc., Vol. 124, No. 8, page 1240 (1977).